Answer:
52 km/h
Explanation:
When the two trucks move together after collision, the momentum of the system is conserved. The kinetic energy is not conserved. This is inelastic collision
The formula to apply here is :
māvā + māvā = {mā+ mā} *vf
Given that ;
mā = 8 ton ----convert to kg [ multiply by 907.185] =7258 kg
vā = 60 km/h
mā = 5 tons ------4536 kg
vā = 40 km/h
vf = final velocity
Using the values given;
māvā + māvā = {mā+ mā} *vf
8*60 + 5*40 = {8+5} * vf
480 + 200 = 13 * vf
680 = 13vf
680/13 = vf
52 km/h = vf